Idiopathic osteoarthritis of the hip: incidence, classification, and natural history of 272 cases.

Long-term clinical and radiographic data of 210 patients (272 hips) with idiopathic hip osteoarthritis were reviewed. Of the 272 hips, 218 (80%) were eccentric and 54 (20%) were concentric. In eccentric hips, the femoral head migrated superolaterally or superomedially, because of the eccentric development of the degenerative changes, which had deteriorated rapidly. Hips with eccentric idiopathic osteoarthritis underwent total hip arthroplasty (THA) at an average of 4 years after symptom onset. In concentric hips, the femoral head migrated medially, causing progressive thinning of the medial wall of the acetabulum, and degenerative changes progressed slowly. Hips with concentric idiopathic osteoarthritis underwent THA at an average of 10 years after symptom onset.